1. Field of the Invention
The present invention relates to a high intensity discharge (HID) lamp. More particularly, the present invention relates to an HID lamp capable of switching between a stable mode and a flickering mode after ignition. In the flickering mode, the high intensity discharge lamp has an intensity of illumination alternately varying at a human-visible frequency between a relatively bright state and a relatively dim state, in which the intensity of illumination in the relatively bright state is larger than that in the relatively dim state and the intensity of illumination in the relatively dim state is larger than zero.
2. Description of the Related Art
For commercial and industrial applications, the HID lamps such as metal halide (MH), high pressure sodium (HPS), and high pressure xenon (HPX) lamps have increasingly gained acceptance over incandescent and fluorescent lamps. The HID lamps are more efficient and more cost effective than incandescent and fluorescent lamps for illuminating large open spaces such as construction sites, stadiums, parking lots, warehouses, and so on, as well as for illumination along roadways. However, the conventional HID lamps cannot be operated at a flickering mode wherein their intensity of illumination alternately varies between a relatively bright state and a relatively dim state, resulting in an undesired restriction against an applicable range of the conventional HID lamps.
U.S. Pat. No. 6,448,720 discloses a HID lamp having only one operation mode after ignition, i.e. a constant intensity of illumination. U.S. Pat. No. 6,329,767 discloses a HID lamp having a dimmable intensity of illumination after ignition by using a dimmer, but a function of the dimmer is limited to monotonously reduce the intensity of illumination until zero instead of causing the intensity of illumination to flicker at a predetermined frequency. U.S. Pat. No. 6,448,713 and the prior art described therein disclose a HID lamp provided with a triac-based phase-control dimmer for controlling the intensity of illumination of the HID lamp by controlling a degree of voltage clamping through a duty cycle of output waveforms of the triac. However, a responsive voltage-current (V-I) curve to the dimmer is nonlinear since the HID lamp is driven by an alternating current, so it is difficult for the intensity of illumination to be accurately adjusted to a desired level.
Typically, the HID lamp includes at least an arc-tube containing two electrodes, chemical compounds, and a fill gas. The fill gas can include one or more gases. To initiate operation of the lamp, the fill gas is ionized to facilitate the conduction of electricity between the electrodes. For example, the conventional HPS lamp uses a 2500 to 4000 volt pulse for ignition. If the lamp is extinguished after lamp operation, the lamp cannot be restarted until after the lamp cools down and the fill gas can be ionized again. For many types of HID lamps, this lamp cooling period can be between approximately 40 seconds and 2.5 minutes.
Another method of restarting a HID lamp is to provide a hot restrike ignitor, which has been disclosed in U.S. Pat. No. 6,091,208. The hot restrike ignitor produces a pulse which is higher in voltage and contains significantly more energy than a pulse generated by a standard ignitor. Consequently, if a flickering mode is realized for the HID lamp through a start-extinguish-restart manner, a lifetime of the HID lamp is adversely shortened. Moreover, from an operation safety point of view, it is very dangerous that the restart requires a considerably high voltage each time.
Therefore, the HID lamps are difficult to perform a flickering illumination as compared with the incandescent and fluorescent lamps.
In view of the above-mentioned problem, an object of the present invention is to provide a flickering mode control system for an HID lamp so as to flicker the HID lamp at a predetermined frequency.
Another object of the present invention is to provide a lighting apparatus with a flickering mode, in which an HID lamp serves as a light source, for realizing functional purposes such as indication, warning, defense, or attack, thereby substituting for incandescent and fluorescent lamps and enlarging an applicable range of the HID lamp.
According to one aspect of the present invention, a flickering mode control system for a high intensity discharge lamp includes an alternating-current to direct-current converter, an output power controllable transformer, a direct-current to alternating-current converter, a lamp driver unit, and a flickering control unit. The output power controllable transformer receives a direct current power supply and outputs a direct current signal. The output power controllable transformer is provided with a switch and determines a power of the direct current signal on the basis of an ON/OFF clock pulse signal for controlling the switch. Based on the a lamp current feedback signal received from between the output power controllable transformer and direct-current to alternating-current converter and a flickering activation signal received from the outside for operating the HID lamp at the flickering mode, the flickering control unit for outputting a power modulation signal as the ON/OFF clock pulse signal to the switch of the output power controllable transformer for controlling the power of the direct current signal to vary at the human-visible frequency.
According to another aspect of the present invention, a lighting apparatus with a flickering mode includes an HID lamp serving as a light source, and a flickering mode control system, thereby realizing functional purposes of indication, warning, defense, or attack through the flickering mode.
The flickering mode control system according to the present invention operates the HID lamp at the flickering mode in which the HID lamp has an intensity of illumination alternately varying at a human-visible frequency between a relatively bright state and a relatively dim state. The intensity of illumination of the HID lamp is extremely small in the relatively dim state of the flickering mode, resulting in that it looks like the HID lamp is completely extinguished. However, since the HID lamp is actually not extinguished in the relatively dim state of the flickering mode, there is no problem associated with the restart of the HID lamp. Therefore, the HID lamp is capable of operating at the flickering mode without a use of a hot restrike ignitor, thereby enhancing the lifetime of the HID lamp and the operation safety.
Since the flickering mode realizes the functional purposes such as indication, warning, defense, or attack, the range of applications of the HID lamp is expanded. Therefore, the present invention facilitates the HID lamp 20 to thoroughly substitute for incandescent and fluorescent lamps.